(a) (i) State the collision theory of reaction rates. (ii) Using the collision theory, explain...
(a) (i) State the collision theory of reaction rates.
(ii) Using the collision theory, explain briefly how temperature can affect the rate of a chemical reaction.
(b) (i) Sketch a graphical representation of Charles’ law.
(ii) Calculate the volume of oxygen that would be required for the complete combustion of 2.5 moles of ethanol ats.t.p.
[molar volume at s.t.p = 22.4 dm\(^3\)]
(c) (i) Defineesterification.
(ii) Give two uses of alkanoates.
(iii) Give the products of the alkaline hydrolysis of ethyl ethanoate.
(d) A tin coated plate and a galvanized plate were exposed for the same length of time.
(i) Which of the two plates corrodes faster?
(ii) Explain briefly your answer in 2 (d) (i).
Explanation
(a)(i) States that atoms, molecules/ions / particles / reactants involved in a chemical
reaction must collide before reaction can take place.
(ii) When temperature is increased/decreased the reacting molecules gain / lose kinetic energy and move faster / slower.
Frequency of collision and effective collision increases/decreases therefore rate of reaction increases/decreases.
(The explanation must correspond to score)
(ii) C\(_6\)H\(_5\)OH\(_{(aq)}\) + 3O\(_{2(g)}\) → 3H\(_2\)O\(_{(l)}\) + 2CO\(_{2(g)}\)
From the equation 1 mole of ethanol requires 3 x 22.4 dm\(^3\) of oxygen
2.5 mols = \(\frac{2.5 \times 3 \times 22.4}{1}\)
= 168.0 dm\(^3\)
(c) (i) Esterification is the reaction between an alkanol and alkanoic acid to produce an alkanoate / ester (and water in the presence of a mineral acid.)
(ii) - used as solvents (e.g. for paints, nail, varnishes, lacquer, adhesives and
cellulose nitrates)
- used in perfumes/cosmetics
- used in (artificial) flavouring for foods
- production of soap
- plasticizers
(iii) ethanol / C\(_2\)H\(_5\)OHand sodium ethanoate (CH\(_3\)COONa) / potassium ethanoate(CH\(_3\)COOK)
(d)(i) Tin – coated plate
(ii) Zinc is more reactive than tin / higher in the electrochemical series than tin. When the tin coated plate is exposed, the plate goes into solution / corrodes. In zinc coated (galvanized) plate, it is the zinc that dissolves / corrodes hence protecting the plate better and zinc coated plate does not corrode.